This invention relates to a unit adapted to be used with an automatic packaging machine for heat sealing the tops of upright pouches which have been filled with product by the machine. Such a unit usually comprises a pair of elongated and generally horizontal sealing bars disposed on opposite sides of the pouch and adapted to be momentarily moved into engagement with the top portion of the pouch. Both bars usually are heated and thus the sealing is effected by the heat and pressure applied by the bars.
The invention more particularly relates to a unit for sealing pouches which either have been filled with a liquid food product and/or which are purged with steam after having been filled. A packaging machine in which the pouches are filled with food product and then are purged with steam is disclosed in Johnson U.S. Pat. No. 4,081,942.
Some difficulty is encountered in sealing pouches which have been filled with liquid food product and/or purged with steam. When droplets or particles of food product and/or droplets of condensate are present in the seal area of the pouch, blisters and blemishes may be formed in the seal when heat is applied to the pouch by the sealing bars. The problems presented by contamination of the seal areas are discussed in detail in Schultz et al U.S. Pat. No. 3,673,041 and Wilson U.S. Pat. No. 3,830,681.